Motion transmission system



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MOTION TRANSMISSION SYSTEM Original Filed May 13, 1944 2 SHEETSSHEET 2 FIG. 4

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IN VEN TOR. THOMAS O. M CARTHY ATTORNEY Patented Feb. 19, 1952 UNITED STATES 'PATENT OFFICE MOTION: TRANSMISSION SYSTEM Thomas OConnell McCarthy, Pawl ing, N. Y.

Original application May 13, 1944, Serial No. 535,529. Divided and this application January 6, 1949, Serial No. 69,546

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) This invention relates to electrical systems for transmitting angular motion that include a transmitter unit and one or more repeater units. This application is a division of my copending application entitled Compass Correction System,

Serial No. 535,529, filed May 13, 1944, aban-- doned. The subject matter of the abandoned application is described and claimed in my copend ing application "Compass Correction System, Serial No. 104,122, filed July 11, 1949, now Patent No. 2,581,428 granted January 8, 1952, as a continuation of said abandoned application.

A well-known type of such a system includes transmitter and repeater units which are usually alike and each comprises a single-circuit field winding and a polycircuit armature winding, one of which constitutes a stationary element known as the stator and the other a movable element known as the rotor. The field windings of the transmitter and repeater are excited from a suitable source of alternating current and the respective armature windings are connected to-' gether.

These systems are used for many purposes and, under normal conditions, the repeater unit will follow the transmitter unit faithfully. In other words, motion of the transmitter throu-h a 30 angle will cause the repeater to move through a. 30 angle in the same direction, and so on.

In certain applications of angular-motiontransmission systems, it is desired not to have the repeater follow the transmitter degree for degree. For example, in a remote-reading compass system it is desirable to introduce a correction for the well-known compass errors. Likewise in direction-transmitting systems such as used in ordnance for target designation, the transmitted direction must be modified to allow for horizontal and for vertical parallax before the gun, range finder, or searchlight will point at, the target being designated by the locator- "instrument. Similarly, in radio-direction finders there exists an error that resembles a deviat on error found in the compass art and that is, in fact, called a deviation error. This error can be corrected, compensated for, or removed so as to provide a direction indication that is ap-. proximately true. Many other installations incorporating direction-transmission systems are known wherein it is likewise desirable to provide a controllable asynchronous relation between the transmitter and repeater units.

general object of this invention, thelffifore, s to provide a n w and i p ed pp r tu IQ! Gil 2 efiecting a controllable asynchronous relation between the transmitter and the one or more repeater units of an angular-motion-transmitting system.

Another object is to provide an apparatus of the type described wherein the amount of the asynchronism between the transmitter and repeater units varies as a function of the instant angular position of the transmitter unit.

A further object is to provide a new and improved electrical device for connection between the transmitter and repeater units of a synchro system wherein the normal synchronous relat on existing between the rotorelements of these units is made asynchronous by an amount that varies as a desired function of the instant angular position of the rotor element of the transmitter unit relative to its stator element.

Another object of this invention is to provide an improved and automatic electrical com pensator for angular-motion-tr nsmission s sterms that is much less costly than the pres nt known mechanical compensators and that is a so exceedingly simple in construction and operation. Furthermore, through simple adjustment means, the character of the compensation effected by the device can be alter d over a very wide range to provide almost any action required.

Another object is to provide a new and improved apparatus that a tomatically com ensates for the deviation error in remote-reading com ass systems.

A further object of the invention s to erovide a new and improved apparatus that automatically compensates for the deviation error in an earth-inductor-compass system.

A still further object of the invention is to provide a novel type of construction for a control transformer.

Another object is to provide a novel means of combining electrical and mechanical ouantities.

These and other ob ects of the invention w ll become more apparent from the d tailed description to follow and the accompanying drawings which show preferred embodiments of the invention in which:

Fig. 1 is a diagrammatic view of the invention as applied to a flux-gate earth-inductorcompass system;

Fig. 1a is a perspective view of a control transe former according to the present invention with the windings omitted in the interest of clare. s;

Fig. 2 is a view of the primary and secondary coil arrangement in one leg of the flux-gate;

Fig. 3 is a perspective view of the gyro-stabilized flux-gate; and

Figs. 4, 5, and 6 are plots of the deviation, correction and resultant curves for the apparatus in Fig. 1.

In Figs. 1-3, inclusive, there is shown diagrammatically an earth-inductor-compass system constructed according to the present invention. A saturable core transformer, or flux-gate, indicated by numeral I0, consists of three legs, I I', I2 and I3, arranged to form an electrical equilateral triangle in space. All of these legs are of the same construction and each of them (see Fig. 2) such as leg I I consists of a primary winding IIa, secondary winding IIb, and a pair of closely adjacent cores Ho and H11.

As shown in Fig. 2, the primary winding Ila is divided, one half being wound on core He and the other half on core IId.' The two halves of the primary are wound in opposite directions and they are thus non-inductive. The primary Winding Ila is excited from a source of alternating current which, in the present embodiment, has a frequency of 487 cycles per second obtained from a suitable oscillator I4 (Fig. l) of conventional design and therefore shown only in block diagram.

The primary windings I'Ia, I20 and I3a are designed to saturate their respective cores twice during each cycle, and for most of the cycle. During the saturation period there is, of course, no transformer action between the primaries and their associated secondaries. During each of the two unsaturated periods of the cycle, there is still no transformer action between the primary and secondary windings insofar as concerns the component of current in the primary from the 487 cycle per second source because the two halves of each primary winding are wound in opposite directions. However, during each of the unsaturated periods, the earth's flux E cuts through both halves of the core in the same direction and therefore induces a voltage in each secondary winding, a frequency twice that of the primary, or 975 cycles per second.

As shown in Fig. 3, the three legs of flux-gate may be enclosed in a casing III, which is mounted in gimbals and stabilized by a gym in order to maintain it horizontal in the earth's field E. A suitable arrangement is shown in the U. S. Patent to A. A. Stuart, Jr., No. 2,361,433, patented October 31, 1944, to which reference is made for a fuller disclosure thereof.

The amplitude of each of the three voltages induced in the secondaries Ilb, I2b and I3b depends on their instant position relative to the direction of the earth's field. These voltages therefore vary with the instant heading of the aircraft, vessel or other carrier upon which the flux-gate is mounted. As the compass is rotated in the earth's flux, the three voltages vary in a manner similar to the voltage variations caused by movement of the rotor in a conventional synchro system.

I It should be pointed out that the magnitude of the induced voltages in these secondaries, which, as shown, may be delta connected, is very small, being of the order of a few microvolts. Hence, it is necessary to connect the output thereof to a Y-connected stator I5 of a coupling Autosyn I 6. The rotor element I1 of the Autosyn is provided with a single-circuit W1 3!- the induced voltage having ing and the voltage induced therein by the currents in its polycircuit stator windings is amplified in amplifier I8, of conventional construction, and transmitted to the variable-phase winding I! of a two-phase stator element of a low-inertia induction motor 20. The other phase Winding Iila of the stator is connected to the 9'75 cycle per second alternating-current output terminals on oscillator I4. Induction motor 20 has a squirrel-cage rotor 2 I.

Rotors I1 and 2I are mechanically coupled together by a shaft 22. Hence the voltages impressed upon the stator windings I9 and I9a of motor 20 will cause its rotor 2| and rotor I! to rotate until the latter reaches its null position. Induction motor 20 is therefore a torque amplifier which turns rotor I 1 to the position it would take were it able itself to develop the necessary torque.

From what has been described so far, it is seen that a change in angular position of the flux-gate IIl relative to the earth's field effects a like angular change in the position of rotors I1 and 2I and the shaft 22 connected therebetween. The flux-gate II) is therefore analagous to the transmitter unit of a synchro or self-synchronous system and the motors I5 and 20 analagous to a repeater unit of such system.

For repeating the instant angular position'of rotors I1 and 2|, a second self-synchronous system is utilized and comprises a, transmitter "unit 23 and one or more repeater units 24.

The transmitter and repeater units are similar in structure, although the repeater would normally be smaller than the transmitter if the latter is to drive a number of repeater units.

The transmitter unit 23 includes a permanentmagnet rotor 25 coupled to shaft 22 and a statorincluding a' circular, laminated core. The stator has an exciting coil 2'! wound upon it with a lead tapped off at each point, thus making four leads altogether: two input leads and two tapped leads. The constants of the transmitting unit (the number of turns, value of exciting current, and magnetic alloy selected for the stator core) are chosen so that the stator core will be completely saturated twice during, and for most of, each cycle of its supply source,.which has a frequency of 400 cycles per second. During periods of saturation, no inductive effect can be produced within the core by the exciting current or the permanent-magnet rotor. However, during each of the short unsaturated periods of the core, the rotor is free to produce an inductive effective upon it. During these periods, the rotor's magnetic flux flows through the core, and as it does'so, induced voltages are superimposed in the stator winding. These voltages are at a frequency of 800 cycles per second since the stator core is rendered unsaturated for a short period twice during each cycle. The voltages across the taps of each of the three parts of the stator winding differ in value and vary with the instant position of the rotor 25 relative to stator winding 21.

As previously stated, the repeater unit 24 is similar to transmitter unit 23 and its rotor and stator winding are identified by reference numerals 28 and 29', respectively.

The stator windings 21 and 29 of the transmitter and repeater units 23, 24 are connected in parallel and excited from the same 400 cycle per second alternating-current source."

When the rotors 21, 29 of units 23,-'24 are n the same position relative to theirresped tive stator windings, the three tapped voltages induced in the stator'win'dings 21 and 29 are alike. However, when the rotor 25 is rotated by shaft 22, the induced voltages in the stator winding 21 will difler from those in the stator winding 29 causing signal current to flow from winding 21 to winding 29 superimposed upon the excitation current. This flow of current produces a new resultant magnetic flux in the stator winding 29 causing the rotor 28 of the repeater unit to rotate until it is in the same relative position to its stator winding 29 as the rotor 25 in the transmitter unit is to its stator winding 21. Accordingly, any angular displacement of rotor 25 by rotation of shaft 22 causes a like displacement of rotor 28.

' It is now seen that as the bearing of the carrier for the flux-gate i0 changes relative to the earth's field, such bearing change will be fed electrically through the Autosyn coupling iii and induction motor producing an equal angular change in the position of shaft 22 and of the rotor in the transmitter unit 23, which angular change may be indicated by a pointer 30. Transmitter unit 23 is then, in effect, a master compass. The position of pointer 30 may then be repeated by a pointer 3| on the rotor element of the one or more repeater units 24.

The earth-inductor-compass and all other types of compass systems depending upon the earth's magnetic flux for direct indications fail to indicate the true geographic north by the algebraic sum of the variation and deviation errors. Variation, which is the angle between the true or geographical and the magnetic meridians, is known for any given locality. The devi ation is the total angular difference between the magnetic meridian and the indications of the compass system, and is caused by the magnetism of the vessel or other carrier upon which the compass system is carried.

The remoteereading earth-inductor-compass system that has been described thus far is exceedingly practical since the magnetically sensitive element (flux-gate Hi) can be mounted a so as to eliminate the effects of the unsymmetrical iron and steel of the compass carrier, such as are found in a vessel, and in-a location where the eilects of horizontal soft iron will be of a low value. deviation error is reduced to a factor, that, when plotted as an ordinate against compass indication as an abcissa, results in a curve having sinusoidal characteristics. shown in Fig. 4.

In the earth-inductor compass that has been described, the bearing indication on the transmitter unit 23 would, if not compensated, be in error by the algebraic sum of the variation and deviation errors. In this invention no compensation for variation is contemplated because this component of the total error is a constant for any latitude in which. the compass carrier may be. However, one way for compensating the variation error would be to provide some means for shifting the rotor 25 of the transmitter 23 relative to shaft 22.

However, this invention does provide an automatically operating and novel corrector or compensator which will substantially cancel out the deviation component of the total error.

Automatically operated deviation compensators presently known are of a mechanical nature and most costly, and in no case do they alter the compensation to match the change in deviation A. typical curve is Whenthis condition is obtained, the

error caused by displacement in. magnetic latitude of the carrier. This invention substitutes anelectrically-operated compensator that is far more simple and less costly.

In particular, and with reference to Fig. 1. one form of my improved deviation compensator comprises a wave generator 32 and a control transformer device 33. The wave generator 32 consists of a flux-gate element which is similar to any of the three legs of flux-gate .ill. That is, the'generator 32 includes two cores 32a and 32b of a material having a high permeability with a primary winding 32c split between them, the .two halves of this winding being wound on their respective cores in opposite directions -so as to be non-inductive with respect to thesecondary winding 32d which surrounds primary.

intensity and direction. The earth's field is obviously also present in the cores 32a and 32b but its intensity, when compared to that of magnet 34, is so minute that it can be totally disregarded so far as operation of generator 22 is concerned.

Like ilux-gate Ill, the two cores 32a and 32b are saturated twice durlng,.and for almost .the entire period of, each cycle. However, during the two short periods in each cycle when cores 32a, 32b are unsaturated, the entry of the magnetic field from magnet 34 into these cores eifects a transformer action to induce a voltage into the secondary 32d. The frequency of the voltage output from the secondary 32d is twice that of the primary, or 975 cycles per second since the cores 32a, 32b are saturated twice during each cycle.

Transformer 33 includes a rotatable primary winding 33a and a pair of secondary windings 33b, 330 which may be wound on suitable circular cores and tapped at the points. The outputs from secondary windings 33b and 330 are connected in parallel and applied by means of conductors 35, 36, and 31 to the stator winding l5 of coupling Autosyn IS. The primary winding 33a is fed the output of the secondary winding 32d of the wave generator 32. Consequently, when current flows in primary 33a, a voltage is induced in each of the three divisions of secondaries 32b and 33c between the 120 tap points, the amplitude of each such voltage being dependent in part'upon the particular angular position at which the rotatable primary winding 33:: is set relative the secondary windings 32b and 320. I

For increased flexibility of adjustment, one of the secondary windings, that at 33b, is-supported for rotation in either direction and also for vertical adjustability. The other secondary winding 33c is fixed in a given position. Thus, the amplitude of the voltages induced at the 120 tap points are adjustable according to the instant adjust mentof the rotor 33a, in view of preliminary adjustrnents that may be made in winding 331:. Any convenient and suitable arrangement can be used for mounting the transformer windings 33a, 33b and 330 to provide the desired adjustability. One such arrangement is shown in Fig. 1a and consists-'of-an' axial support 49 on which are mounted toroidal cores 5|, and core 55 which is of substantially figure-B-shaped construction.

Core 5| is preferably fixed to the axial support l3; cores 53 and 55 are mounted for rotation thereabout and translation therealong. For this purpose, the core 53 is provided with a hub 51 from which extend radial spokes 53 to support the core 53. Hub 5! is manually slidable over and rotatable on the axial support 49, and may be secured at any desired position by means of setscrew 6|.

Core 55 is provided with an upstanding collar 63 afllxed thereto. which is manually slidable and rotatable on support 49. The core 55 can be secured at any desired position by tightening a setscrew 65. Coils 33a, 33b and 33c wound on cores 55, 53 and 51, respectively, are not shown in Fig. 1a to avoid complication of the drawing.

The means disclosed for providing the desired adjustability of the coils 33a and 33b are merely exemplary and any other suitable means can be employed. If necessary or desired, conventional sliding electrical contacts can be used between the lead wires and the windings to avoid twisting and mutilation thereof.

The three voltages at the 120 tap points, which are the correction voltages to compensate for the deviation error, are, as noted above, connected into the electrical connections between the secondary windings llb, 12b, I32) and stator windings 45 of the coupling Autosyn It by means of conductors 35, 36 and 31 and series-connected variable resistors 38, 33 and 40.

During the operation of the flux-gate system, a very complex flow of current exists between the secondaries of the flux-gate element I and the stator elements ii of the coupling Autosyn It. This current changes for every angular position of the flux-gate with respect to the earths field. A part, at least, of the current flowing between the flux-gate element and stator element I is thought to circulate through the secondaries of the transformer 33, reacting, in turn, upon the primary of this transformer andcausing the current flowing therein to vary in strength as the flux-gate element rotates in the earth's field. The output electromotive force of the transformer unit, accordingly, varies as a function of the angular displacement of the compass or earth inductor.

In the system shown in Fig. 1, the primary winding 320 of generator 32 is excited at onehalf the frequency of the voltageoutputs from secondary windings Ilb, 12b and I312 of the fluxgate l0. As this frequency is doubled by wave generator 32, the correction voltages from transformer 33 will be at the same frequency as the output voltages from secondaries II b, |2b and Nb. As the excitation for both flux-gate I0 and generator 32 is derived from the same source, oscillator l4, and transformer 33 is electrically coupled to generator 32, a predeterminable but controllable phase relationship exists between the deviation correction voltages and the output voltages from flux-gate I0.

It should now be apparent that if good compensation for the deviation component of the total compass error is to be obtained, correction voltages must be derived that, if applied to an earth-inductor-compass system without a compensator and located on a vessel or other carrier having no iron whatsover, would produce a curve'such as that shown in Fig. 5. Theoretically, this curve should be such that were it to be combined algebraically with the curve in Fig. 4, the net result would be zero error around the entire horizon. Although the theoretically desired curve is possible, it has been found in practice that a correction curve that only approximates the contour of the deviation curve and will therefore produce the resultant curve such as that shown in Fig. 6 is satisfactory. Such a curve can be obtained by varying the position of the primary 33a relative to the secondaries 33b and 330 associated therewith and making such adjustments as may be necessary in the settings of resistors 38, 39 and 40 in circuit with the secondary windin of transformer 33, and resistor 4| in circuit with the primary of generator 32. The points at which the correction curve crosses the base line can be adjusted by shifting the position of primary winding 33a and the amplitude of the curve is adjusted through resistors 384|, inclusive. For compounding two curves of varying amplitude and frequencmadjustment of winding 33b can be made. For further controlling of the amplitude of the correction voltages or the shape of the correction curve, a phase shifting device in the form of a'variable capacitor 42 in the primary circuit of the correction transformer 33 may be used.

As the heading of the carrier on which the compass system is installed changes through 360, the only error will be that shown in Fig. 6 which is within the inherent error of the compass system.

Once the correct position for the primary 33a .of transformer 33 relative to its secondaries 32b and 33c is adjusted for any particular compass installation, it need not be disturbed because it will automatically produce the right amounts of correction voltages required at any instant bearing throughout the 360 range.

As an alternative arrangement, the component parts of the distributed secondary windings 33b and 330 of transformer 33 may be Y-connected instead of connected in delta as shown in Fig. 1.

In an actual correction problem the curve of compass deviation such as shown in Fig. 4 may be obtained by any of the standard well-known methods for the particular ship in which the compass system is to be installed. With these data available it is simple matter to make the necessary adjustments to the corrector circuits to remove the deviation from the system. The compass heading of the ship having been determined, from the curve, for a) each null point and (b) the points of maximum amplitude, the ship is swung so as to be on the heading of a null, and the rotatable primary 33a of the correcting transformer 33 is positioned so that there is no deviation in the compass system for this particular heading. The ship is then swung to the heading of a point of maximum deviation and the primary excitation of the corrector transformer is adjusted to remove all deviation; it will then be found that the deviation will have been removed or reduced to a small value for all headings of the ship. Should finer adjustment be desired a second swing of the ship can be made and the controls readjusted. Should the curve of compass variations be non-symmetrical, it may be necessary to adjust the resistances in the secondary leads from the corrector transformer, and/or impedance in the primary excitation circuit.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be 9 understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Iclaim:

1. An earth inductor-compass system com prising, a flux-gate having a plurality of interconnected flux-gate legs, each leg having primary and secondary windings thereon, electrical indicator means connected to the output of the flux-gate secondary windings for indicating azimuthal position of said flux-gate, a control transformer comprising a primary winding and a pair of relatively adjustable secondary wind ings having a common output, an oscillator having a pair of outputs, one of said outputs being at a frequency double that of the other output, means connecting the lower frequency output to the primary windings of said flux-gate, means connecting the higher frequency output to the primary winding of said control transformer, and means connecting the output of said secondary windings of said control transformer to the output of the flux-gate secondary windings.

2. An earth-inductor-compass system comprising, earth-induction means including a plurality of saturable core type transformers for producing from the horizontal component of the terrestrial magnetic field electromotive forces varying in accordance with the amount and direction that said induction means are displaced in azimuth relative to the direction of the terrestrial magnetic field, a source of alternatin current for exciting the primaries of said transformers, means interconnecting the secondaries of said transformers to provide a polycircuit electromotive force output, electrical indicator means including a polycircuit winding for indicating angular displacement of said induction means, electrical connections between the secv ondaries of said transformers and the polycircuit winding of said indicator means, and means for modifying the polycircuit output produced by said induction means as a function of the angular displacement of said induction means to compensate for deviation, last said means comprising a control transformer having a single single circuit primary and at least two relatively adjustable polycircuit secondaries having a common output, means connecting the polycircuit output from the secondaries of said control transformer to the connections between said induction and indicator means, and means for exciting the primary of said control transformer with an alternating current at a frequency double that of the current feeding the primary of said earth induction means.

3. An earth-inductor-compass system comprising, a flux-gate having a plurality of interconnected fiux-gate legs, each leg having primary and secondary windings thereon, electrical indicator means connected to the output of the flux-gate secondary windings for indicating azimuthal position of said flux-gate, a control means for supplying alternating current to the primary windings of said flux-gate and wave generator from a common source, and means connecting the output of the secondary windings of said control transformer to the output of the secondary windings of said flux-gate.

4. An earth-inductor-compass system comprising a polycircuit earth induction means having primary and secondary windings for deriving from the horizontal component of the terrestrial magnetic field electromotive forces varying in accordance with the amount and direction that said induction means are displaced in azimuth relative to the direction of the earth's magnetic field, polycircuit electrical indicator means for indicating the angular displacement of said induction means, electrical connections between said induction and indicator means, and means for modifying said electromotive forces, last said means comprising a transformer having a single circuit primary and a pair of relatively adjustable ploycircuit secondaries, means connecting the output from said polycircuit secondaries of said transformer to said electrical connections, means providing a relatively strong unidirectional magnetic field, wave generating means re sponsive to said relatively strong unidirectional magnetic field for producing an electromotive force alternating in synchronism with the varying electromotive forces derived from the secondary of said induction means, and means coupling said alternating electromotive force to said transformer primary.

THOMAS OCONNELL MCCARTHY.

REFERENCES orrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,525,563 Baker Feb. 10, 1925 1,527,488 Onwood Feb. 24, 1925 1,584,670 Slepian May 11, 1926 1,613,222 Curtis Jan. 4, 1927 1,964,265 Markley June 26, 1934 2,045,831 Carbonara June 30, 1936 2,405,050 Pfunter et al. July 30, 1946 2,452,862 Neff Nov. 2, 1948 2,472,546 Pomeroy June 7, 1949 FOREIGN PATENTS Number Country Date 368,280 Great Britain Feb. 22, 1932 

